1. Field of the Invention
The present invention relates to a semiconductor device and a method for manufacturing the same, and more specifically to a semiconductor device having a semiconductor device chip mounted on a circuit substrate and encapsulated with resin, and a method for manufacturing the same.
2. Description of Related Art
In a prior art semiconductor device, a method has been performed in which a semiconductor device chip is mounted on one principal surface of a circuit substrate, and solder bump electrodes is formed on the other principal surface of the circuit substrate by locating a solder ball on electrodes formed on the other principal surface of the circuit substrate, and by reflowing the solder ball. This method is widely known as a BGA (Ball Grid Array). This package is attracting attention, since it has a construction fitted to a package required to have a number of electrodes.
In the case of forming the solder bump electrodes on the circuit substrate as an external electrodes of the package, since the solder bump electrode is required to have a height, a method of directly putting a solder ball on the electrodes of the circuit substrate has been performed in the prior art.
For example, Japanese Patent Application Pre-examination Publication No. JP-A-02-284426 discloses a method for forming a solder bump electrode on a predetermined electrode by means of a solder immersing method, although it relates to a semiconductor device chip itself.
As shown in FIG. 1, this prior art example is so constructed that an aluminum electrode 15 having poor solder wettability is formed on a silicon oxide film 14 formed on a silicon substrate 13, and a whole surface of the aluminum electrode 15 exposed within an opening formed in an insulator film 16 is covered with a conductive paste 17 having a solder wettability, and an assembly thus formed is immersed into a solder bath so that a solder bump electrode 18 is obtained.
Furthermore, Japanese Patent Application Pre-examination Publication No. JP-A-05-327202 discloses a method for forming a solder bump electrode by printing a solder paste on a predetermined electrode and shaping it by a reflowing.
In the prior art semiconductor device shown in FIG. 1, the conductive paste is formed on the whole surface of the aluminum electrode having poor solder wettability. The reason for this is that it is necessary to cover a large area with the conductive paste, since it is difficult to obtain a sufficient bond strength between a surface of the aluminum electrode and the conductive paste because an oxide film is formed on the surface of the aluminum electrode, and since it is also difficult to obtain a sufficient bond strength between the conductive paste and the solder because of a resin component included in the conductive paste.
In addition, the height of the solder bump electrode obtained by the solder immersing method is on the order 30 .mu.m at maximum in the case of an electrode having one side length of 100 .mu.m. This is effective in the case that the height of the solder bump electrode is not so required as in TAB (Tape Automated Bonding), but has become difficult to apply to a packaging for mounting on a printed circuit substrate. In the method for printing and reflowing the solder paste, on the other hand, it was difficult to obtain a sufficient bump height in comparison with the area in which the solder is printed.